In a spectrophotometer, light emitted from a light source is irradiated onto a sample, and light which has interacted with the sample (transmitted light and the like) undergoes wavelength separation by a spectroscopic element, and the intensity at each wavelength is detected. In such a spectrophotometer, for example, a halogen lamp or deuterium lamp is used as the light source, a diffraction grating is used as the spectroscopic element, and a photodiode array detector is used as the detector.
A photodiode array detector of this sort is used for example in the detection section of a liquid chromatograph. The configuration of the major parts thereof is shown in FIG. 1. Light emitted from a light source 1 is condensed by a lens 2 and irradiated onto a sample cell 3. Components in the sample which have been separated chronologically in an unillustrated column flow into the sample cell 3 along with the mobile phase, absorb light of a specified wavelength, and are then ejected into a drain. Light which has been transmitted through the sample cell 3 passes through a slit 4 and then undergoes wavelength dispersion by a concave diffraction grating 5 and is detected by a photodiode array detector 6. The detection signal from the photodiode array detector 6 is used for identifying sample components or determining the concentration of sample components.
Photodiode array detector 6 comprises, for example, 1000 elements lined up in a one-dimensional array, being arranged such that the light of the shortest wavelength enters the first element and light of the longest wavelength enters the 1000th element. Light which has entered each light receiving element is converted to an electric charge and accumulated. The electric charge which has been accumulated over a predetermined period of time is extracted to form a detection signal. Since there is an upper limit to the amount of electric charge which can be accumulated in a light receiving element, the charge accumulation time is set such that the electric charge accumulated in a light receiving element will not become saturated.
The intensity of the light radiated from a halogen lamp or deuterium lamp differs depending on wavelength. If the charge accumulation time is set with reference to the wavelength at which the intensity of the light emitted from such light sources (hereinafter referred to as “light intensity of the light source”) reaches its maximum, the detection signal in the wavelength region of low light intensity of the light source will be weak and will be buried in noise. Thus, in the prior art, measures have been devised to maintain a high S/N ratio even in the wavelength region of low light intensity by setting the charge accumulation times of the light receiving elements making up the photodiode array detector in accordance with the light intensities of the various wavelength regions (for example, Patent literature 1). Normally, the charge accumulation time of each light receiving element is set to the time at which the charge accumulated in each light receiving element reaches saturation capacity in a state where there is no absorption of light by the sample components (in a state where only the mobile phase is made to flow through the sample cell 3).